FR3032905A1 - COMPOSITE PANEL HAVING AN IMPROVED ASSEMBLY TERMINATION AND STRUCTURE COMPRISING SUCH A PANEL - Google Patents

Abstract

Composite panel (1) comprising an upper skin and a lower skin (10, 11) on either side of a core (12) of foam or honeycomb, which comprises at an edge of the composite panel an assembly termination comprising a reinforcing element (13a, 13b, 13c) integrated in the panel and running along the edge of the panel, the reinforcing element comprising at least a first wall (14a, 14'a, 14 "a) facing one of said skins, at least one second wall (14b, 14c, 14d, 14e) facing the other of said skins and at least one connecting wall (15a, 15b, 15c, 15d, 15e) between said first and second walls, the assembly termination further comprising beyond the reinforcing element a return edge to the skin (17) made by joining together the two skins (10, 11).

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a composite panel for forming a structural element, provided with an improved assembly termination and a structure. including such a panel. The panel of the invention applies to structures comprising sandwich-type composite panels in order to ensure a structural connection between the sandwich composite panel and other elements of the structure, the latter possibly being metal structures or other composite panels. The invention is more particularly applicable to structures of large dimensions in the field, such as for example the walls of rail transport cars. BACKGROUND In general, and as in particular in land transport and in particular the railway field, the links between different structural panels are provided by welded lines by structural rivets or bolted connections. The designers of train structures, as is the case in all areas of transport, seek to reduce the mass of structures in order to increase the payload and / or to reduce energy consumption, while at the same time controlling production costs. It is therefore interesting in the field of land transport to seek solutions using high-performance composite materials, as is the case in the fields of aeronautics and space. 3032905 2 The introduction of structural parts made of high performance composite materials requires the implementation of economical and reliable technical solutions to ensure the mechanical connections between the different subassemblies. The present invention relates to the technical field relating to the assembly of large structures, generally metal, and often sandwich type, or panels consisting of two skins connected by connecting pieces, and more particularly the field of train structures , which will be referred to later in the description.

EP0392828A1 in Figures 4 and 7 to 10 discloses bolted joints between different types of train car body floors and vertical walls of these cases. The example of Figure 4 proposes in particular to make a box with two brackets fixed together and provided with wings of the extruded floor.

Document JP2001278039A proposes to make the junction of a floor with a sandwich panel wall with a square part. US6065261A discloses, in the context of fixing sandwich composite panels with metal tubular panels of light alloys, connecting pieces between said panels made by means of tubular sections provided with support flanges on the metal tubular panels, the latter themselves being provided with wings which are bolted or riveted under a lower face of the tubular sections. For connections with composite sandwich panels, in the aeronautical field there are in particular U-shaped flange devices as shown in Figure 1 and the splinting devices as shown in Figure 2. The bindings are taken over the skins with in the case of Figure 2 a so-called back to skin technique for which the skins protrude from the core and are secured together with a metal plate against. In the context of the prior art, the connection represented in FIG. 2 has the disadvantage of greatly reducing the bending inertia of the structure in the connection zone, which may have an unacceptable weak point. The link shown in FIG. 1 makes it possible to remedy this problem, but at the cost of a large number of connection lines to be achieved, which represents the cycle and therefore the cost. It should be noted that these two examples of bonds have in common the use of a splice, the presence of which requires specific and therefore additional connection lines. Brief description of the invention In the context of the present invention, architecture envisaged for composite structural parts consists of sandwich panels comprising two skins made of composite materials consisting of fibers and synthetic resin based on polymeric material. The skins are glued on each side of a low density core which makes it possible to obtain the desired flexural inertia properties. This type of structure is advantageous in terms of performance and cost. The bonding of these structural parts made of composite materials with complementary structural elements requires a connection making a transition between said panels and said elements taking up the forces undergone by the panels and ensuring the physical integrity of the ends of said structural parts. . The choice of the bonding technology which is the subject of the invention is based on the use of mechanical connection elements such as rivets, blind bolts or screws / nuts and the use of reinforcing inserts. The invention particularly aims to provide a structural connection between a sandwich panel and a metal structure or between two sandwich panels, to preserve optimal bending inertia and minimize the number of fastening lines and therefore the cost of 'assembly.

More specifically, the invention provides a composite panel comprising an upper skin and a lower skin on either side of a foam or honeycomb core, which comprises at an edge of the composite panel a termination of assembly comprising a reinforcing element integrated into the panel and running along the edge of the panel, the reinforcing element comprising at least a first wall facing one of the said skins, at least a second wall facing the other of the said skins and at least a connecting wall between said first and second walls, the assembly termination further comprising at the 3032905 beyond the reinforcing element a return edge to the skin made by joining together the two skins. According to a preferred embodiment, a profile is disposed between the reinforcing element and the edge where the skins meet, said profile being provided with an inclined face at the edge of the structure, said profile forming a tilted draping support realizing a transition face allowing the upper skin to be applied to the lower skin to achieve the border. According to a first embodiment, the reinforcement is a tube of rectangular or square section for which the first and second walls respectively form an upper and lower face of the reinforcement, said faces being connected by side walls of the tube. According to a second embodiment, the reinforcement is an omega profile and comprises a first central wall connected to two second walls by lateral ribs of the omega profile.

According to a first alternative, the internal space of the reinforcement is filled by a material of the same structure as the core of the panel. According to a second alternative, the internal space of the reinforcement is left empty. According to a third embodiment, the reinforcement is a Z-shaped section and comprises a first cantilevered top wall connected to a second bottom wall cantilevered by a connecting wall of the profile. According to a first embodiment, the reinforcement is made of composite material. The composite material of the reinforcement is preferably made of fiberglass or carbon and synthetic resin.

The composite material of the reinforcement advantageously comprises a stack of transverse or circumferential layers at 90 ° and layers inclined at ± 40 ° to 50 ° with respect to a longitudinal axis of the reinforcement. According to a second embodiment, the reinforcement is made in a metal compatible in terms of differential expansion with the polymerization cycle of the composite panel so as not to degrade the collages. The core / reinforcement and skin / reinforcement connections are preferably made with a film adhesive but can also be made with a self-adhesive resin.

The invention further proposes an assembly of a composite panel according to the invention forming a first structural element with a second structural element which comprises a connecting element comprising a profile provided with a bearing surface and fixing the element on the panel at the first wall 5 of the reinforcement, a connecting face and a bearing face and fixing on the return edge to the skin of the panel. In the case where the composite panel has a transition face, the connecting face along the transition face. The connecting element is preferably part of a structural element to be attached to the composite panel. The invention further relates to an assembly of two composite panels according to the invention disposed opposite head to tail at their assembly ends, fastening means fixing the edges of the return to the skin of each of said panels on the reinforcement of the panels opposite through a face 15 of said opposite panel. BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the invention will become apparent upon reading the following description of a nonlimiting exemplary embodiment of the invention with reference to the drawings which represent: FIG. example of fixing a structural element of the composite panel type with a connecting element according to the prior art; in FIG. 2: an example of bonding two composite panels by splicing of the prior art; in FIG. 3: a sectional view of a composite panel termination 25 according to a first embodiment of the invention; in Figure 4: a sectional view of an exemplary assembly device according to the invention of the panel of Figure 3 with a structural element; FIGS. 5a, 5b, 5c, 5d show sectional views of exemplary embodiments of panels according to various embodiments of the invention; In Figure 6: a sectional view of an alternative assembly device of the invention; In Figure 7: a junction of two panels according to the invention. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION FIGS. 1 and 2 show prior art connection devices, in particular in the aeronautical and space field. FIG. 1 relates to a sandwich / metal connection with a "U" flange where the panel A is taken up between two plates B and C, the plate C being attached and fixed on a connecting piece D 5 comprising the plate B. FIG. represents a sandwich / metal connection by splicing with return to the skin. The splint is fixed on the returns to the skin H1, H2 of two composite panels Gl, G2. The connection shown in FIG. 2 has the disadvantage of greatly reducing the flexural inertia of the structure in the connection zone, which may have a weak point that is not acceptable by the design. The connection shown in Figure 1 does not pose this problem, but at the cost of a large number of connection lines to achieve and the presence of a splint. The bonding principle of the invention based on a reinforcement integrated in the panel is described in FIG. 3 and the main elements constituting the fixing end of the panel are shown in FIG. 4. The composite panel 1 comprises two skins in composite 10, 11 in particular made of fiberglass and / or carbon associated with a synthetic resin, for example an epoxy resin whose thicknesses and draping are optimized to ensure the mechanical strength requirements and stiffness of the panel. It comprises a core material 12 preferably polyethylene (PET) foam, polymethacrylimide (PMI), aluminum honeycomb or aramid fiber known under the trademark Nomex. The completion of the termination includes a hollow or solid end profile 16. The profile, which can be made of the same material as the core, is provided with an inclined face at the edge of the structure. The slope of the inclined face 25 provides an inclined layup support adapted to allow a skin 10 to be applied to the other 11 by a progressive transition for example along a slope between 30 ° and 60 ° to the zone back to the skin 17 where the skins are superimposed. In FIG. 3, the skins are represented before bonding or polymerization, in particular at the return to the skin 17. Examples of polymerized terminations are shown in particular in FIGS. 5A to 5D. According to FIG. 5A, the profile is cut into a triangle and according to FIG. 5D, the profile comprises a section provided with a rectangular portion under an upper wall 14 "a of the reinforcement and a triangular portion between the edge of the wall 3032905 The core / skin connections 20 are made with a film adhesive or a self-adhesive resin and a reinforcing element 13a is integrated during the manufacture of the panel parallel to the edge of the panel separated from said edge by the profile.

The reinforcing element 13a in the form of a square or rectangular tube integrated into the panel and bordering the edge of the panel has a first wall 14a facing one of the skins, a second wall 14b facing the other of the skins and two walls. link 15a, 15b between said first and second walls. The assembly termination comprising beyond the reinforcing element a return edge to the skin 17 made by joining together the two skins 10, 11 and the profile 16 cut in a triangle is disposed between the reinforcing element 13a and the edge 17 where the skins meet, said section forming an inclined draping support providing a transition face 21 allowing the upper skin to be applied to the lower skin to achieve the edge.

The reinforcement is made of a metal compatible in terms of differential expansion with the polymerization cycle of the composite panel so as not to degrade the collages. With reference to FIG. 4, a device for assembling a composite panel type element 1 with a second structural element 20 comprises a connecting element 31 comprising a profile provided with a support face 32 and fixing the element on the panel at the first wall 14a of the reinforcement 13a, a connecting face 34 and a face 33 of support and attachment to the edge 17 back to the skin of the panel. The connecting face 34 runs along the transition face 21 and the first support face 25 is on one side of the panel while the second side is on the opposite side of the panel. In the case of FIG. 6, the connecting element 31 is integral with a structural element 35 to be fixed to the composite panel whereas in the case of FIG. 6, the panel of the invention is fixed directly on a terminal folded sheet 30 forming a metal panel. In the case of FIG. 4, the connecting element 31 is fixed to the panel at the level of the reinforcement and the edge by blind bolt-type fastening means 40, 41 as well as in the case of FIG. , the bolt fixing the connecting element at the reinforcement. In the case where the skins of the sandwich panel are made from carbon fibers, the fixing means are preferably made of stainless steel materials (type A286) and / or titanium alloy type TA6V to ensure compatibility. of the assembly device with respect to galvanic corrosion. The fastening means are chosen either with protruding head 40 or countersunk head 41.

The functions of the reinforcement 13a are to reinforce locally the inner skin vis-à-vis the local forces of tearing induced by the blind bolt, to provide protection of the outer skin vis-à-vis the degradation induced during drilling (delaminating out of hole) and / or forming the bulb of the blind bolt, to diffuse the localized tearing force at the level of the blind bolt 15 towards the core material and to the external composite skin and to mechanically resume the compressive forces introduced locally by the connection, instead of the foam whose compression resistance is low. Figure 7 shows the assembly of two panels of the invention head to tail.

According to this example, first fixing means 401 pass through the edge 17 'of a first 1' of the two composite panels, the skin 11 provided with the transition slope of the second 1 of the two panels and the reinforcement 13a of this second panel and second fasteners 402 pass through the edge 17 of the second of the two panels, the skin 11 'provided with the transition slope of the first of the two panels and the reinforcement 13'a of this first panel. A filling element 42 catches the game at one of the two fasteners. Several reinforcing geometries may be provided provided to connect the two skins of the sandwich panel and to have a width sufficient to allow the installation of the fasteners. Several examples of reinforcing geometries are shown in Figures 5A-5D as examples. According to FIG. 5A, the reinforcement is a tube 13a of rectangular or square section for which the first 14a and the second 14b walls respectively form an upper and lower face of the reinforcement, said faces being connected by lateral walls 15a, 15b of the tube. According to FIGS. 5B and 5C the reinforcement is an omega section 13b and comprises a first central wall 14a 'connected to two second walls 14c, 14d by lateral ribs 15c, 15d of the profile. In the case of FIGS. 5A and 5B, the space inside the profile can be left empty. In the case of Figure 5C the internal space of the profile is filled by a material 18 of the same structure as the core of the panel.

In the case of Figure 5D the reinforcement is a Z-shaped section 13c and has a first cantilevered top wall 14a 'connected to a second cantilevered bottom wall 14e through a connecting wall 15e of the profile. In configurations where the reinforcement is not supported by a core material, in the case of FIGS. 5A and 5B, it is necessary to ensure the mechanical strength of the profile under the pressure and temperature constraints induced by the material. polymerization cycle of the sandwich panel. The reinforcement preferably consists of fiberglass or carbon fibers depending on the applications associated with a resin (epoxy for example). Differential expansion compatibility of the composite and reinforcement materials will be ascertained. The reinforcement may also be made of metal material, provided also to verify in this case the compatibility in terms of differential expansion with the polymerization cycle of the composite panel so as not to degrade the collages. For example, if the composite is a carbon fiber composite, the metal may be a nickel iron steel known as INVAR. Indeed, if a differential expansion between the profile and the composite skins exists, they will mainly appear in the direction of the length during the rise in temperature and will generate internal stresses in the bonded bonds during cooling. These constraints can weaken the assembly, warping or at worst lead to breaking adhesives including panels longer than ten meters like panels making a continuous wall of rail car body.

The stack of the reinforcement preferably consists of circumferential layers (90 °) and longitudinal layers ± a (for example ± 45 °), in a proportion that may be 50% for one and the other. The thickness of the wall will be of the order of magnitude of that of the skins, being of the order of 2 to 4mm.

The reinforcement may be an already polymerized profile; or it can be made in situ during the manufacture of the sandwich panel and polymerized at the same time as the latter. The connecting elements preferably consist of blind bolts in view of the lack of access to the interior of the "A" structure (and also potentially "C" to ensure the passage of a tightening wrench. connecting elements may be chosen to protruding heads or countersunk heads in case of requirement of a smooth profile on the outer face of the box for example, so as to mask the presence of the heads under the paint Return to Figure 4, the complementary structure element 35 on which the panel is mounted may be made of a metallic material, for example in the case of a connection with an existing body structure of aluminum alloy or steel. In this case, it will take up the constructive principles of the composite panel of the invention, given the fact that the connection is hyperstatic, a functional game of composite material. e mounting is to be taken into account at one of the two wings 32, 33 of the link. This functional clearance can be filled before or after the bonding elements have been put in place by a filler material 42. The solution may for example consist in interposing a liquid resin in the set to be filled and then in carrying out the hardening cycle of this resin. This resin will preferably consist of an epoxy base (for example known under the trademark Hysol EA9394 or other equivalent solutions) loaded to withstand the compressive stresses in the joint. The use of this resin may also be carried out by injection into the gap after docking. Another solution is to deposit a layer of liquid sealant in one of the two parts before docking, the docking efforts to ensure the creep mastic.

Another solution for filling is to use solid shims and interpose them in the air gap, but this requires an additional operation to measure the residual clearance followed by disassembly of the connection, which is a disadvantage in terms of assembly cost in relation to the liquid filling solution. The present invention can be used in particular on all types of road transport vehicles or rail passenger transport, for which structural connections are required. The invention is not limited to the example shown and in particular one or more edges of the structure 10 may be provided with the assembly device of the invention. In the case of a four-sided structure, the reinforcements can be made in the form of a continuous frame.

Claims (4)

CLAIMS1 - Composite panel (1) comprising an upper skin and a lower skin (10, 11) on either side of a core (12) made of foam or honeycomb, characterized in that it comprises at the level of of an edge of the composite panel 5 an assembly termination comprising a reinforcing element (13a, 13b, 13c) integrated in the panel and along the edge of the panel, the reinforcing element comprising at least a first wall (14a, 14'a) , 14 "a) facing one of said skins, at least one second wall (14b, 14c, 14d, 14e) opposite the other of said skins and at least one connecting wall (15a, 15b, 15c, 15d , 15e) 10 between said first and second walls, the assembly termination further comprising beyond the reinforcing element a skin return border (17) made by joining together the two skins (10, 11). 2 - Composite panel according to claim 1 wherein a profile (16) is disposed between the reinforcing element (13a, 13b, 13c) and the border (17) where the 15 skins meet, said section being provided with a face inclined at the edge of the structure, said section forming an inclined draping support providing a transition face (21) allowing the upper skin to be applied to the lower skin to achieve the edge. 3- composite panel according to claim 1 or 2 wherein the reinforcement is a tube (13a) of rectangular or square section for which the first (14a) and the second (14b) walls respectively form an upper and lower face of the reinforcement, said faces being connected by lateral walls (15a, 15b) of the tube. 4 - composite panel according to claim 1 or 2 for which the reinforcement is an omega profile (13b) and comprises a first central wall (14a ') connected to two second walls (14c, 14d) by lateral ribs (15c, 15d). ) of the omega profile. Composite panel according to claim 3 or 4 wherein the internal space of the reinforcement is filled by a material (18) of the same structure as the core of the panel. 6 - Composite panel according to claim 3 or 4 for which the internal space of the reinforcement is left empty. 7 - Composite panel according to claim 1 or 2 for which the reinforcement is a Z-shaped section (13c) and comprises a first cantilevered upper wall (14a ') connected to a second cantilevered second wall (14e) by a connecting wall (15e) of the profile. 8 - Composite panel according to any one of the preceding claims wherein the reinforcement is made of composite material. 9 - composite panel according to claim 8 wherein the composite material of the reinforcement is made of fiberglass or carbon and synthetic resin. 10 - Composite panel according to claim 8 or 9 wherein the composite material of the reinforcement comprises a stack of 90 ° transverse or circumferential layers and layers inclined at ± 40 ° to 50 ° with respect to a longitudinal axis of the reinforcement. 11 - Composite panel according to any one of claims 1 to 7 wherein the profile is made of a metal compatible in terms of differential expansion with the polymerization cycle of the composite panel. 12. Composite panel according to any of the preceding claims wherein the core / reinforcement and skin / reinforcement (20) connections are made with a film adhesive or a self-adhesive resin. 13 - Assembly of a composite panel according to any one of the preceding claims forming a first structural element with a second structural element characterized in that it comprises a connecting element (30, 31) having a profile provided with a face (32) for supporting and fixing the element on the panel at the level of the first wall (14a, 14'a, 14 "a) of the reinforcement, a connecting face (34) and a face ( 33) for supporting and fixing the edge (17) to the skin of the panel 14 - An assembly according to claim 13, wherein the composite panel comprising a transition face according to claim 2, the connecting face ( 34) along the transition face (21) - An assembly according to claim 13 or 14 for which the connecting element is part of a structural element (35) to be fixed to the composite panel 3032905 14 16 - Assembly of two composite panels according to one of Claims 1 to 12, characterized in that e the panels are arranged opposite head to tail at their assembly terminations, fixing means (401, 402) fixing the edges of return to the skin (17, 17 ') of each of said five panels on the reinforcement (13a , 13'a) of the opposite panel through a face (11, 11 ') of said opposite panel.